GB1565089A - Combined fuel injection pumps and injection nozzles for diesel engines - Google Patents

Description

PATENT SPECIFICATION

( 21) Application No 53795/76 ( 11) 1 565 089 ( 22) Filed 23 Dec 1976 ( 31) Convention Application No 2558789 ( 32) Filed 24 Dec 1975 in ( 33) Fed Rep of Germany (DE) ( 44) Complete Specification Published 16 Apr 1980 ( 51) INT CL 3 ( 52) F 02 M 57/02 Index at Acceptance F 1 B 2 J 11 B 2 J 15 A 2 2 J 15 B 2 2 J 15 C B 102 B 228 BA F 1 A 1 C 2 2 A 2 C 2 A 6 3 F 1 A 3 K 4 K ( 54) IMPROVEMENTS IN OR RELATING TO COMBINED FUEL INJECTION PUMPS AND INJECTION NOZZLES FOR DIESEL ENGINES ( 71) We, ROBERT BOSCH GMBH, a German Company, of Postfach 50, 7 Stuttgart 1, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the

following statement:

The invention relates to a high-pressure fuel injection device for diesel engines.

Such devices are known which have an hydraulically driven pump and injection nozzle, particularly a combined injection pump and injection nozzle, for each working cylinder of the engine A piston of the pump is driven by a servo-piston of larger diameter, one end of which servo-piston defines a servo-pressure chamber which, by way of a change-over valve controlled in synchronism with the engine, is connectible to a pressure source producing the hydraulic servo-pressure when the changeover valve is in one switching position, and is connectible to a return line when the valve is in its other switching position The injection nozzle has a valve needle which is loaded by a closing spring disposed in a spring chamber and is additionally loadable by the servo-pressure by way of an overflow passage and opens a valve seat when moved in the opposite direction to the direction of flow of the fuel.

In one such known fuel injection device of this type in the form of a combined injection pump and injection nozzle, the servopressure loading the valve needle acts as an hydraulic spring and influences the opening pressure and the closing pressure acting upon the injection nozzle In another such known injection device, the closing spring of the injection nozzle is additionally subjected to the servo-pressure whose pressure level is in turn variable for the purpose of varying the injection pressure of the fuel injection device in the form of a combined injection pump and fuel injection nozzle and thus also varies the hydraulic spring acting on the valve needle in proportion to the servopressure or injection pressure The two known injection devices have the disadvantage that the servo-pressure acting as an hydraulic spring increases the opening pressure and the closing pressure of the injection nozzle by the same amount.

Extremely short injection times are required in modern, heavy-duty diesel engines and, moreover, the injection operation should be stopped abruptly, within a crank angle of 1 if possible since the delayed termination of the injection operation, and the after-injection which frequently occurs, impair the combustion and lead to an increased emission of CH and CO A favourable course of combustion is obtained when the injection operation commences at a relatively low injection nozzle opening pressure and thus with a short injection jet, and is increased to maximum pressure towards the end of the injection operation with an injection jet of correspondingly greatest length, and then ceases abruptly.

However, owing to the hydraulic and mechanical conditions at the fuel injection device, abrupt closing of the needle is very difficult to realise.

Therefore, an object of the invention is to obtain rapid closing of the needle of the injection nozzle and at the same time to influence the course of injection so as to increase the injection pressure towards the end of the injection operation.

According to the present invention there is provided a high pressure fuel injection device for each working cylinder a diesel engine, the device comprising a hydraulically driven pump and an injection nozzle, the pump comprising a pump piston and a servo-piston of larger diameter for driving the pump piston, a servo-pressure chamber being defined by one end of the servo-piston and being connectible, by means of a 0 h O 1 565 089 change-over valve adapted to be controlled in synchronisism with the engine, to a source of hydraulic servo-pressure when the change-over valve is in one switching position, and to a return line when the said valve is in its other switching position, the injection nozzle comprising a valve needle displaceable in an opening direction opposite to the direction of flow of the fuel against the force of a closure spring, the valve needle being additionally loadable by pressure in a pressure chamber which is located in the region of that end of the valve needle which is remote from the valve seat and in which the servo-pressure as controlled by the change-over valve is applied via a pressure passage to increase the closing force on the needle valve.

Thus, a hydraulic increase in the closing pressure is obtained at the injection nozzle and becomes fully effective only towards the end of the injection stroke and thus, at the same time, the course of injection is influenced in the desired manner, that is, owing to the coupling to the pressure in the servo-pressure chamber, the additional hydraulic force has a characteristic corresponding to the injection pressure of a hydraulically driven piston pump which is initially proportional to the opening pressure of the nozzle and attains its maximum value at the end of the stroke The opening pressure for the nozzle and the cross section at the nozzle can be freely chosen irrespective of the increased closing force for the nozzle which can be obtained, and the prestress of the closure spring of the valve needle can be reduced in conformity with the additional hydraulic force already acting at the commencement of the injection operation The fuel injection device is provided with a simple construction in that the pressure chamber is formed by the spring chamber accommodating the closure spring.

The invention will hereinafter be further described by way of example, with reference to the accompanying drawings, in which:Figure 1 is a simplified illustration of a first embodiment of a fuel injection system including a fuel injection device in accordance with the present invention, Figure 2 shows a combined injection pump and injection nozzle of a second embodiment of the present invention, also illustrated in a simplified form, and Figure 3 shows a combined injection pump and injection nozzle of a third embodiment of the present invention.

A combined injection pump and injection nozzle is designated 10 in the high-pressure fuel injection system illustrated in Figure 1 and essentially comprises a hydraulically driven piston pump 11 and an injection nozzle 12, the piston pump 11 being constructed, in a known manner, as a servopiston pump, that is it has a differential piston comprising a servo piston 13 and a pump piston 14 One end face 15 of the servo-piston 13 acts as a movable wall to define one end of a servo-pressure chamber 16 to which fuel is fed under servo-pressure (ps) from a pressure source 17 by way of a feed line 18, a change-over valve 19, and a control line 21.

The pressure source 17 producing the servo-pressure essentially comprises a regulable high-pressure feed pump 23 driven by the motor 22, and a pressure-limiting or pressure-regulating valve 24 The highpressure feed pump 23 is fed by a lowpressure feed pump 25 which draws the fuel from a reservoir 26 and feeds it to the high-pressure pump 23 by way of a filter 27, the feed pressure of the feed pump 25 being limited by a further pressure-limiting valve 28 Two further pressure units 31 and 32 (further described hereinafter) are supplied with fuel by the feed pump 25 by way of a branch line 29.

The change-over valve 19 is in the form of a slide valve and its control valve spool 33 is accommodated in the head of the combined injection pump and injection nozzle 10 and, when in its illustrated normal position, connects the servo-pressure chamber 16 to the feed line 18 subjected to servo-pressure, wherein a first annular chamber 34 of the change-over valve 19 which is connected to the feed line 18 is connected by way of a reduced portion 33 a of the control valve spool 33 to a second annular chamber 35 connected to the servo-pressure chamber 16 by way of the control line 21 The control valve spool 33 is movable into its second switching position (not illustrated) against the force of a spring 38 by means of a control pressure pulse which is produced by the pressure unit 31 in synchronism with the engine 22 and which is fed to a pressurecontrol chamber 37 by way of a line 36.

When in this switching position, the servopressure chamber 16 is connected by way of the control line 21, the annular chamber 35 and the reduced portion 33 a to a third annular chamber 40 of the changeover valve 19, the annular chamber 40 being connected to a return line 39 which opens into the connection between the feed pumps 25 and 23 and is thus subjected to the pressure of the fuel delivered by the feed pump 25 it will be appreciated that, alternatively, the return line 39 can lead back directly to the reservoir 26 so that only atmospheric pressure prevails in this line.

In a known manner, the pressure unit 31 can be in the form of a rotary distributor or a piston pump or, alternatively, a device which is controlled by a solenoid valve and which, by relieving the pressure in the control pressure chamber 37, causes the 1 565 089 control valve spool 33 to move into its illustrated position and thus initiates the commencement of injection at which servofuel is fed to the servo-pressure chamber 16.

The second pressure unit 32 acts as a delivery quantity metering device and is connected by way of a line 41 and a non-return valve 42 to a pump working chamber 43 defined by the pump piston 14.

Any optional quantity-controlled injection pump can act as the delivery quantity metering device and, as illustrated, is driven by the motor 22 The two pressure units 31 and 32 will be further described hereinafter, since they are not directly embraced by the invention.

When the pump piston 14 is in its illustrated position, communication between the pump working chamber 43 and the injection nozzle 12 is interrupted and two annular chambers 45 and 46 in the wall of a pump cylinder 47 accommodating the pump piston 14 are interconnected by way of a passage 44 in the pump piston 14, the annular chamber 45 being connected by way of an injection pressure passage 48 to a pressure chamber 51 adjacent to the valve seat 49 in the valve housing 50 of the injection nozzle 12 The annular chamber 46 is connected to a line 54, leading to the return line 39, by way of a relief bore 53 provided with a throttle 52, so that, when the pump piston 14 is in its illustrated position, the pressure chamber 51 in the injection nozzle 12 is relieved towards the return line 39.

The valve seat 49 of the injection nozzle 12 is, in a known manner, closed between the injection operations by means of a valve needle 56 which opens the valve seat 49 by movement in the opposite direction to the direction of flow of the fuel and against the force of a closure spring 55.

A spring chamber 57 which accommodates the closure spring 55, and which is adjacent to that end 56 a of the valve needle 56 which is remote from the valve seat 49, is connected to the control line 21 by way of a pressure passage 58, so that the pressure prevailing in the servo-pressure chamber 16 is introduced into the spring chamber 57, for increasing the closing pressure, and exerts upon the valve needle 56 a force proportional to the pressure in the servo-pressure chamber 16 Alternatively, the pressure can be transmitted to the valve needle 56 in a known manner by way of a pressure transmision piston sealingly guided in the housing 50 of the injection nozzle 12, so that the pressure is stepped up (not illustrated).

Thus, after the completion of the injection operation, the full servo-pressure ps holds the valve needle 56 on its valve seat 49, and the pressure in the spring chamber 57 drops to the pressure prevailing in the return line 39 only upon commencement of the filling stroke of the two pistons 13 and 14, i e when the control valve spool 33 is in its second switching position (not illustrated), and the valve needle 56 is now maintained in its closed state by the closure spring 55 and the reduced pressure in the spring chamber 57 until, by the changingover of the control valve spool 33 into its illustrated position, the servo-pressure ps prevailing in the feed line 18 is introduced into the servo-pressure chamber 16 by way of the change-over valve 19 and the pumping stroke of the pump piston 14 commences The pressure prevailing in the servo-pressure chamber 16 at the commencement of the pumping or injection stroke is determined by the opening pressure and the characteristic of the injection pressure at the injection nozzle 12 and attains its maximum pressure only at the end of the injection stroke, which maximum pressure is then also introduced into the spring chamber 57 by way of the pressure passage 58 and displaces the valve needle 56 onto its seat 49 This rapid closing of the valve needle 56 is further assisted in that, shortly before the end of the stroke or simultaneously with the deceleration of the pump piston 14 the annular chamber 45 is connected to the return line 39 by way of the passage 44 in the pump piston 14 and the relief bore 53 and thus relieves the pressure chamber 51 in the injection nozzle 12 The described function requires the pressure passage 58 to be connected in the region of the servo-pressure chamber controlled by the change-over valve 19 In the example described the pressure passage is connected in a control line 21 located between the annular chamber 35 and the servo-pressure chamber 16 Alternatively, the pressure passage might be connected to the annular chamber 35 or to the upper region of the servo-pressure chamber 16.

A pressure-control device 61 is incorporated in the pressure passage 58 and comprises a throttle 62, or alternatively a pressure control valve may be provided to replace the throttle 62, and a non-return valve 63 which is connected in parallel with the throttle 62 and which opens towards the spring chamber The throttle 62 or the alternative pressure-control valve is arbitrarily adjustable or is adjustable in dependence upon engine operating characteristics such as speed and/or load, whereby the fuel pressure remaining in the spring chamber 57 is adjustable, that is the opening pressure for the nozzle can be regulated in dependence upon engine characteristics, or the pressure-control valve is adjusted such that a desired hydraulic pressure in excess of the pressure in the return line 39 remains in the spring chamber 57 for increasing the closing pressure and, at the commencement of 1 565 089 injection, provides, in addition to the closure spring 55, a hydraulic force which is then boosted by the rising pressure in the servo-pressure chamber 16 during the course of injection A second pressurecontrol device 64 may be incorporated in the pressure passage 58 if the pressure introduced into the spring chamber 57 and acting to increase the closing pressure, is also to be controlled, regulated or arbitrarily adjusted in dependence upon the aforementioned engine operating characteristics relative to the pressure prevailing in the servo-pressure chamber 16 The pressure-control device 64 is constructed in the same manner as the pressure-control device 61, although it includes a non-return valve opening from the spring chamber 57 to the control line 21 and a throttle 66 or alternatively a pressure-control valve, which controls the inflow to the spring chamber 57 According to the desired formulation of the injection characteristic, the two pressure-control devices 61 and 64 or, alternatively, only one or neither of the pressurecontrol devices, can be incorporated in the pressure passage 58 It is also possible to fit only a single throttle 62 in the pressure passage 58 if it is only desired to influence the pressure entering the spring chamber 57.

The second embodiment differs from the first embodiment of Figure 1 only by virtue of the fact that a combined injection pump and injection nozzle 10 a is of different construction from the combined pump and injection nozzle 10 The same parts are provided with the same reference numerals.

The change-over valve 19 and the piston pump 11 are identical to the corresponding parts of the combined pump and injection nozzle 10 However, the injection nozzle designated 12 a essentially differs from the injection nozzle 12 of Figure 1 in that a pressure chamber 71 of a device 72 for increasing the closing pressure is isolated from the spring chamber 57 by means of an intermediate piston 74, as described and claimed in British Patent Application No.

53599176, which is sealingly guided in the valve housing 73 The intermediate piston 74 extends into that end of the spring chamber 57 which is remote from the valve needle 56 and, before the commencement of injection, is at a predetermined distance h from the valve needle 56 When the pressure chamber 71 is connected to the return line 39, the intermediate piston 74 is urged by means of a return spring 75 and the closing spring 55 of the injection nozzle 12 a into its illustrated starting position which determines the distance h from the valve needle 56 Alternatively, according to the matching of the pressures and the piston diameter, the closing spring 55 can solely assume the function of the return spring If, as is illustrated, the valve needle 56 does not have its own stroke stop, the distance h is equal to the needle stroke and the intermediate piston 74 acts as a stroke stop for the valve needle 56.

In the second embodiment of Figure 2, the pressure chamber 51 of the injection nozzle 12 a which is adjacent to the valve seat 49 is also connected to the return line 39, and thus relieved of pressure, by way of the passage 44 in the pump piston 14, the relief bore 53 and the line 54.

In the third embodiment illustrated in Figure 3 the relief bore 53, is not connected directly to the line 54 but is connected to the spring chamber 57 by way of a passage 76.

The pressure in the spring chamber 57 is then limited by means of a pressure-control valve 77 or is regulated in dependence upon engine operating characteristics such as speed and/or load The spring chamber 57 is connected by way of the pressure-control valve 77 to the line 54 leading to the return line 39 In this case, direct communication between the relief bore 53 and the line 54 is interrupted In the case of multi-cylinder engines, one pressure-control valve 77 is sufficient for all the combined pumps and injection nozzles which are connected by way of a line 78 If in a modification the closure spring 55 is supported in the valve housing 73, i e in the spring chamber 57, and the intermediate piston 74 is not loaded by the return spring 75, the servo-pressure prevailing in the control line 21 acts to provide a closing force upon the valve needle 56 by way of the intermediate piston 74 at the commencement of injection, so that the force acting upon the valve needle 56 in the closing direction follows the characteristic of the injection pressure during each injection operation The closure spring 55 can be of correspondingly weaker design, and the peak pressure acts, in a desired manner, upon the valve needle 56 after the end of injection and leads to abrupt closing of the needle.

Although, in the second embodiment, (Figure 2) the relief bore 53 is not connected to the spring chamber 57 by way of a passage 76, the pressure of the fuel leaking into the spring chamber can, nevertheless, be controlled or regulated by means of the pressure-control valve 77.

In the three embodiments shown in Figures 1 to 3 the servo-pressure taken downstream of the change-over valve 19 produces at the injection nozzle an increase in the closing pressure which is proportional to the injection pressure and which leads to the desired abrupt and rapid closing of the needle and thus to the termination of injection.

Claims (18)

WHAT WE CLAIM IS:-

1 A high-pressure fuel injection device 1 565 089 for each working cylinder of a diesel engine, the device comprising a hydraulically driven pump and an injection nozzle, the pump comprising a pump piston and a servopiston of larger diameter for driving the gump piston, a servo-pressure chamber eing defined by one end of the servo-piston and being connectible, by means of a change-over valve adapted to be controlled in synchronism with the engine, to a source of hydraulic servo-pressure when the change-over valve is in one switching position, and to a return line when the said valve is in its other switching position, the injection nozzle comprising a valve needle displaceable in an opening direction opposite to the direction of flow of fuel against the force of a closure spring, the valve needle being additionally loadable directly or indirectly by pressure in a pressure chamber which is located in the region of that end of the valve needle remote from the valve seat and in which the servo-pressure as controlled by the change-over valve is applied via a pressure passage to increase the closing force on the valve needle.

2 A high pressure fuel injection device as claimed in claim 1, in which the closure spring is disposed in the pressure chamber which thereby serves as a spring chamber.

3 A high-pressure fuel injection device as claimed in Claim 1, in which the closure spring is disposed in a spring chamber isolated from the pressure chamber by an intermediate piston sealingly guided in the valve housing.

4 A high-pressure fuel injection device as claimed in Claim 3, in which the intermediate piston is subjected to a return spring force which urges the piston into a starting position at a predetermined distance from the valve needle when the pressure chamber is connected to the return line.

A high-pressure fuel injection device as claimed in Claim 4 in which the return spring force is exerted by the closure spring.

6 A high-pressure fuel injection device as claimed in any of the Claims 3 to 5, in which the predetermined distance between the valve needle and the intermediate piston is equal to the stroke of the needle.

7 A high-pressure fuel injection device as claimed in any of Claims 3 to 6, in which the pressure chamber of the injection nozzle which is adjacent to the valve seat is connectible to the spring chamber shortly before the end of the stroke of the pump piston in a manner controlled by the pump piston.

8 A high-pressure fuel injection device as claimed in Claim 7, in which the pressure in the spring chamber is regulable in dependence upon engine operating characteristics.

9 A high-pressure fuel injection device as claimed in Claim 8, in which the engine operating characteristics are speed and/or load.

A high-pressure fuel injection device as claimed in any of the preceding claims, in which a pressure-control device is fitted in the pressure passage.

11 A high-pressure fuel injection device as claimed in Claim 10, in which the pressure-control device comprises a throttle or pressure-control valve.

12 A high-pressure fuel injection device as claimed in Claim 11, in which the throttle or pressure-control valve controls the return flow from the pressure chamber and is combined with a non-return valve opening towards the pressure chamber.

13 A high-pressure fuel injection device as claimed in Claim 12, in which the throttle or pressure-control valve controls the inflow to the pressure chamber and is combined with a non-return valve opening from the pressure chamber to the control chamber.

14 A high-pressure fuel injection device as claimed in any of Claims 11 to 13, in which the throttle or pressure-control valve is arbirarily adjustable or is adjustable in dependence upon engine operating characteristics such as speed and/or load.

A high-pressure fuel injection device as claimed in any of Claims 2 and 7 to 14, in which a pressure transmission piston, sealingly guided in the valve housing is interposed between the spring chamber and the valve needle.

16 A high-pressure fuel injection device for a diesel engine constructed and adapted to operate substantially as hereinbefore particularly described with reference to and as illustrated in Figure 1 of the accompanying drawings.

17 A high-pressure fuel injection device for a diesel engine constructed and adapted to operate substantially as hereinbefore particularly described with reference to and as illustrated in Figure 2 of the accompanying drawings.

18 A high-pressure fuel injection device for a diesel engine constructed and adapted to operate substantially as hereinbefore particularly described with reference to and as illustrated in Figure 3 of the accompanying drawings.

W.P THOMPSON & CO, Coopers Building, Church Street, Liverpool L 1 3 AB, Chartered Patent Agents.

Printed for Hcr Majesty's Stationery Office, by Croydon Printing Company Limited Croydon Surrey, 1980.

Published by The Patent Office, 25 Southampton Buildings, London, WC 2 A l AY, from which copies may be obtained.